This invention is based on and claims priority to Japanese Patent Application No. 2000-219522, filed Jul. 19, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
This invention relates to a personal watercraft, and particularly to an improved engine control system for a personal watercraft.
2. Description of the Related Art
Personal watercraft have become popular in recent years. This type of watercraft is sporting in nature and carries a rider and possibly one or more passengers. A relatively small hull of the personal watercraft commonly defines a rider""s area above an engine compartment. An internal combustion engine frequently powers a jet propulsion unit that propels the watercraft. The engine lies within the engine compartment in front of a tunnel (e.g., a recess) formed on the underside of the watercraft hull. The jet propulsion is located within the tunnel and is driven by a driveshaft. The driveshaft usually extends between the engine and the jet propulsion device through a wall of the hull tunnel.
Personal watercraft often are operated in a planing state at wide open throttle. In a planning state, the hull of the personal watercraft supports the weight of a watercraft by planing or xe2x80x9cskippingxe2x80x9d over the surface of the water. However, if the speed of the personal watercraft suddenly decreases, the planing hull typically begins to xe2x80x9cdigxe2x80x9d into the water, and drag on the hull significantly increases. If the speed of the watercraft continues to drop, the watercraft hull will experience less and less planing support, and will eventually essentially operate as a displacement-type hull and the speed of the watercraft will be significantly reduced. Personal watercraft usually begin to plane at engine speeds of approximately 2000-3500 RPM.
While planing, it is not uncommon for the personal watercraft to jump out of the water. When this occurs, the engine speed suddenly increases because the hull is no longer substantially affected by water resistance. If this occurs, the engine speed can exceed a maximum value. This is generally undesirable and can result in damage to engine of the personal watercraft. As such, some personal watercraft include engine speed or xe2x80x9crevxe2x80x9d limiting arrangements. In such arrangements, the engine speed is reduced when an engine speed sensor indicates that the engine is operating at an engine speed greater than the maximum value.
Personal watercraft are commonly powered by two-cycle engines, which have the advantage of being fairly powerful and relatively light and compact. However, two-cycle engines typically produce exhaust gases with relatively large quantities of carbon monoxide and various hydrocarbons. To reduce these emissions, personal watercraft typically include an exhaust system with a catalyst for cleaning the exhaust gases. One disadvantage of using a catalyst in a personal watercraft is that if the exhaust gases exceed a maximum temperature (e.g., 1000xc2x0 C.), the catalyst can be damaged and/or the effectiveness of the catalyst is impaired. Such high exhaust gas temperatures can occur when the personal watercraft is planing for long periods at wide open throttle or if the engine speed suddenly increases such as when the watercraft jumps out of the water as described above.
An aspect of the present invention is the realization that prior art engine speed limiting arrangements tend to cause the personal watercraft to suddenly decelerate from the planing state. This is generally undesirable. As such, a need exists for a personal watercraft with an improved engine control system that prevents damage to the engine and/or the exhaust system without causing the personal watercraft to decelerate from the planing state.
One aspect of the present invention is a method for operating an engine speed limiting arrangement of a small watercraft. The small watercraft includes a hull, an internal combustion engine, at least one engine condition sensor and an electronic control unit, which is in electrical communication with the engine condition sensor. The hull defines an engine compartment in which the engine is supported. The method comprises sending a signal from the engine condition sensor to the electronic control unit, determining if the engine condition sensor indicates an abnormal engine condition, and regulating an engine speed of the engine such that the engine speed remains between a maximum value above which the engine can be damaged and a minimum value below which the watercraft will no longer stay in a planing state. In one modified embodiment, the engine condition sensor is a temperature sensor positioned in an exhaust system of the watercraft. In such an embodiment, the abnormal engine condition can be an exhaust gas temperature above 1000xc2x0 C. In another modified embodiment, the engine condition sensor is an engine speed sensor. In such an embodiment, the abnormal engine condition can be an engine speed above 7500 revolutions per minute.
Another aspect of the present invention is a small watercraft that comprises a hull, an internal combustion engine and. an engine speed limiting arrangement. The hull defines an engine compartment in which the engine is supported. The engine speed limiting arrangement comprises an engine condition sensor and an electronic control unit that is operatively connected to the engine condition sensor. The electronic control unit is configured to receive a signal from the engine condition sensor to determine if the engine condition sensor indicates an abnormal engine condition, and to regulate the engine speed of the engine such that the engine speed remains between a maximum value above which the engine can be damaged and a minimum value below which the watercraft will no longer stay in a planing state. In one modified embodiment, the engine condition sensor is a temperature sensor positioned in an exhaust system of the watercraft. In such an embodiment, the abnormal engine condition can be an exhaust gas temperature above 1000xc2x0 C. In another modified embodiment, the engine condition sensor is an engine speed sensor. In such an embodiment, the abnormal engine condition can be an engine speed above 7500 revolutions per minute.
Yet another aspect of the present invention is a small watercraft that comprises a hull, an internal combustion engine and an engine speed limiting arrangement. The hull defines an engine compartment in which the engine is supported. The engine speed limiting arrangement comprises means for regulating an engine speed of the watercraft so as to alleviate an abnormal engine condition without causing the watercraft to drop below a planing speed. In one modified embodiment, the abnormal engine condition is an exhaust gas temperature that exceeds a maximum value. In another modified embodiment, the abnormal engine condition is an engine speed that exceeds a maximum value.
Further aspects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments.